This invention relates generally to a picture frame and, more particularly, to a novel corner joining system for picture frames.
There exist a number of commercially available picture frames and frame sections formed from extruded metal such as aluminum. These picture frames often are available in unassembled kit form. The most common technique for assembling the picture frame sections into the complete frame includes the provision of channels on the rear surface of the frame sections, with the channels of adjacent sections in the corners of the frame meeting in L-shaped configuration. Typically, the adjacent ends of the frame sections have been assembled, to form a corner of the frame, by placing an L-shaped bracket at each corner of the frame so that each leg of the bracket extends into the channel of one of the adjacent frame sections. Each of the bracket legs is secured to its associated framing section by suitable locking means, usually a screw which is threaded through the leg of the bracket and which is urged firmly against the rearwardly facing, inner surface of the channel formed on the rear surface of each framing member.
Because, in the above described arrangement, the set screws are forced against the relatively soft aluminum frame section under considerable pressures, the aluminum tends to become pitted or marred and thus damaged. This becomes a significant disadvantage particularly when the frame is to be used repeatedly as is frequently the case. One of the features of these frames is that they may be assembled and disassembled with relative ease to facilitate changing of displays. Once the rearward facing surface of the web becomes marred the alignment of the frame sections becomes untrue and the rigidity of the corner joints is impaired. This aggravates the not uncommon condition found in such framing devices in which the forwardly facing surfaces of the beveled ends of the frame sections may not mate properly even when the surfaces of the bracket retaining channel are unmarred.
Described in U.S. Pat. No. 4,122,617 is a corner joining system that obviates the tendency of the screws to mar the channel. That system includes a bearing plate formed from a relatively hard material such as steel and having no holes receptive to the set screws. The bearing plate is interposed in the channel interiorly of the screw bearing bracket. When the set screws are tightened, they bear directly against the plate and not against the softer aluminum frame section. The relatively localized force applied by the set screws to the bearing bracket are distributed evenly across the area of the bearing bracket to the regions of the frame section which are engaged by the bearing bracket. This provides a more effective grip on the framing members over a considerably greater area than had been previously achieved merely by the set screws alone. The relatively hard nature of the bearing bracket virtually eliminates the difficulties heretofore presented by applying the force of the set screws directly against the relatively soft aluminum. The frame may be assembled and disassembled any number of times without deterioration of the alignment or effective locking features of the frame.
Although eliminating the marred channel problem, the system disclosed in U.S. Pat. No. 4,122,617 does exhibit certain disadvantages. For example, the use of a bearing plate adds the cost of additional components and entails additional assembly steps. Another deficiency of prior corner joining systems is that excessive penetration of a corner bracket by a set screw will prevent entry of the bracket into a frame section channel during assembly. In that event, the set screw must be backed off before assembly can be completed.
The object of this invention, therefore is to provide an improved corner joining system for picture frames.